Evaporative cooling system

ABSTRACT

The evaporative cooling system comprises: evaporative cooling modules, a liquid supply system which comprises a liquid supply pump and a tube, and which supplies a refrigerant liquid to the evaporative cooling modules; an air supply system which comprises air supply tubes, and which supplies warm air to the evaporative cooling modules; an exhaust system which comprises an exhaust pump and a tube, and which exhausts air containing a refrigerant vapor from the evaporative cooling modules; a reflux system which comprises a primary heat exchanger and a reflux tube, and which condenses the refrigerant vapor to return the condensed refrigerant liquid to the liquid supply system; and a heat exhaust system which comprises a secondary heat exchanger and tubes, and which discharges heat absorbed from the primary heat exchanger.

INCORPORATION BY REFERENCE

The present application claims priority from Japanese application JP2007-149882 filed on Jun. 6, 2007, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to a cooling system for a heating element,and more particularly to an evaporative cooling system suitable forinformation platform apparatuses such as a server, a network, and astorage which are required to have higher performance and higherdensity.

Conventionally, evaporative cooling is known as means for efficientlycooling heating elements, such as a processor, an LSI, electronicdevices, power devices, and dynamic devices. The evaporative coolingutilizing latent heat of refrigerant is considered promising forimproving the cooling efficiency and reducing the weight and size ofcooling system, as compared with air cooling and liquid cooling whichutilize heat conduction and heat transfer from a heating element torefrigerant.

For example, air cooling, water cooling, and evaporative cooling arecompared with each other in the case where a heating element of 100 W iscooled. It is assumed that the specific heat and density of air are 1.0J/g·K, and 0.0012 g/cm³, that the specific heat, density, and heat ofevaporation of water are 4.2 J/g·K, 1 g/cm³, and 2300 J/g, and that thetemperature rise of refrigerant in air cooling and water cooling is 30K. The weight ratio between the refrigerants necessary for cooling theheating element on this assumed condition is given as air cooling:watercooling:evaporative cooling=3.3 g/s:0.79 g/s:0.043 g/s=77:18:1, and thevolume ratio between the refrigerants is given as air cooling:watercooling:evaporative cooling=2800 cm³/s:0.79 cm³/s:0.043cm³/s=64000:18:1. Thus, it is seen that evaporative cooling hasextraordinarily high potential performance in comparison with aircooling and water cooling. However, the practical cooling performancelargely depends on supply means, evaporation condition, and the like, ofthe refrigerant.

There are several known examples as the evaporative cooling means.

U.S. Pat. No. 6,085,831 discloses that a semiconductor chip which is aheating element is covered with a jacket, and a refrigerant iscirculated in the inside of the jacket. The refrigerant is circulated inthe inside of the jacket in such a manner that the refrigerant liquid isevaporated by the heating element, that the refrigerant vapor is cooledand condensed by the air cooling fins outside the jacket, and that thecondensed refrigerant liquid is again returned to the heating element.

JP-A-2000-252671 discloses that a circulatory pipe is attached to amicroprocessor which is a heating element. The circulatory system isconfigured in such a manner that a refrigerant vapor evaporated by theheating element is moved in the inside of the pipe, that the refrigerantvapor is condensed in a heat exchanging section configured by aircooling fins, and is separated into a refrigerant liquid and air, thatthe refrigerant liquid and air are respectively fed to a nozzle byseparate pipes, and the refrigerant liquid is sprayed to the surface ofthe heating element by a piezoelectric film from the nozzle, and thatthe refrigerant liquid is again evaporated by the heating element.

U.S. Pat. No. 6,205,799 discloses that a circuit board with asemiconductor device which is a heating element mounted thereon ishoused in a case, and a refrigerant liquid is sprayed to the heatingelement from a sprayer in the case. The refrigerant liquid is circulatedin such a manner that an evaporated refrigerant vapor is fed to a heatexchanger through a pipe connected to the case, and that the condensedrefrigerant liquid is fed to a reservoir by a pump, and is again fed tothe sprayer from the reservoir. The sprayer is configured by a heater, achamber, an opening, and the like, which are formed in a siliconsubstrate in accordance with a thermal ink jet system which is aprinting technique for a printer.

U.S. Pat. No. 6,889,515 discloses that a spray module is attached to asemiconductor which is a heating element, and a coaxial tube isconnected to the module. A refrigerant liquid is circulated in such amanner that the refrigerant liquid is sprayed to the heating elementthrough the inner tube of the coaxial tube from a pump, that arefrigerant vapor is collected from an opening in the module, and fed toa condenser through the outer tube of the coaxial tube, and that theliquefied refrigerant is fed to a reservoir from the condenser, and isagain sprayed to the heating element by the pump.

JP-A-2006-39916 discloses that a vapor generator is attached to a CPUwhich is a heating element. A circulation cycle of a refrigerant isformed in such a manner that a refrigerant is evaporated in thegenerator, and a refrigerant vapor is fed to a condenser connected tothe generator, that the refrigerant is cooled by an air cooling fan tobe liquefied and sent to a receiving tank, and that the liquefiedrefrigerant is again fed to the generator from the receiving tank.

JP-A-11-26665 discloses an example in which a hollow heat sink isattached to a case of a CPU which is a heating element, and arefrigerant is supplied to the inner surface of the heat sink broughtinto contact with the heating element, from a water storage pit insidethe heat sink on the basis of a capillary phenomenon. A circulatorysystem is configured in such a manner that the refrigerant is evaporatedinside the heat sink, and air containing a refrigerant vapor is fed to aheat exchanger and a dehumidifier through a pipe by a fan, that therefrigerant liquefied by the heat exchanger is again returned to thewater storage pit of the heat sink by a pump, and that the air dried bythe dehumidifier is returned to the heat sink by a compressor.

In U.S. Pat. No. 6,085,831 and JP-A-2000-252671, the refrigerant isenclosed in the jacket and the circulatory pipe, and the refrigerantvapor and liquid are mixed in the same space. Thus, there is a problemthat vapor pressure of the refrigerant in the vicinity of the heatingelement is increased to make it difficult to evaporate. Further, thejacket and the circulatory pipe are integrated with the air coolingfins, and thereby the mounting area of such integrated components needto be provided around the heating element. Thus, there is also a problemthat the mounting density of the heating element cannot be increased.

In U.S. Pat. No. 6,205,799 and U.S. Pat. No. 6,889,515, the coolingsystem is configured by the sprayer and the spray module which spray therefrigerant liquid to the heating element, the heat exchanger and thecondenser which condense the refrigerant, the reservoir which stores therefrigerant, the pump which feeds the refrigerant liquid to the spray,and the like. Since the refrigerant vapor and liquid are mixedly fedsimilarly to U.S. Pat. No. 6,085,831 and JP-A-2000-252671, a spraymechanism based on a thermal ink jet and a compressor, needs to beprovided, in order to destroy the saturated vapor layer in the vicinityof the heating element in order to promote evaporation of therefrigerant. Thus, there is a problem that these components hinder theminiaturization and the improvement of reliability of the coolingsystem.

In JP-A-2006-39916, the cooling system is configured by the vaporgenerator attached to the heating element, the condenser based on aircooling, the receiving tank, and the like. However, the refrigerantvapor and liquid are enclosed in the same circulatory system similarlyto U.S. Pat. No. 6,085,831 to U.S. Pat. No. 6,889,515. Thus, there is aproblem that the vapor pressure of the refrigerant is increased in thecirculatory system and thereby the vaporization efficiency is lowered.

In JP-A-11-26665, the cooling system is configured by the hollow heatsink having a substantially same area as that of the heating element,the heat exchanger which cools and liquefies the refrigerant vaporevaporated in the hollow heat sink by the air cooling fan, thedehumidifier which dries the air exhausted from the heat sink, the pumpwhich returns the refrigerant liquid from the heat exchanger to the heatsink, the compressor which sends the dry air from the dehumidifier tothe heat sink, and the like. In the same closed circulatory system asthose in U.S. Pat. No. 6,085,831 to JP-A-2006-39916, the dehumidifier isprovided so that the vapor pressure inside the heat sink is reduced topromote the evaporation of the refrigerant. However, such configurationprevents the miniaturization and weight reduction of the cooling system.Further, the refrigerant liquid and the dry air are supplied to the heatsink in the same direction with respect to the heat sink. Thus, there isa problem that as the evaporation is performed on the front side, thevapor pressure is increased on the back side to thereby make itdifficult to evaporate the refrigerant.

As described above, the conventional techniques have problems that theevaporative cooling efficiency is low and the miniaturization and weightreduction of the cooling system is difficult. An object of the presentinvention is to effect miniaturization and weight reduction of thecooling system by making evaporative cooling efficiently performed, andto realize high performance of the cooling system by improving themounting density of the information platform devices. To this end,according to the present invention, there is provided an evaporativecooling system in which the supply of the refrigerant and atmosphere andthe evaporation condition are optimized on the basis of the principle ofevaporative cooling, and which is suitable for the high mountingdensity.

BRIEF SUMMARY OF THE INVENTION

An evaporative cooling model can be obtained, on the basis of thePenman-Monteith method, by assuming that an evaporation amount isproportional to a difference between saturated vapor pressure and vaporpressure of an atmosphere. When latent heat flux (heat removal densityfrom a heating element) is set as L_(a) (W/cm³), heat of evaporation ofa refrigerant is set as ε (J/g), saturated vapor pressure is set ase_(s) (hPa), vapor pressure of atmosphere is set as e_(a) (hPa), and acoefficient is set as k (g/cm²·s·hPa), the relation between theseparameters is expressed by Expression 1.

L _(a) =k·ε·(e _(s) −e _(a))   (1)

The latent heat flux L_(a) is proportional to the heat of evaporation εand to the difference between the saturated vapor pressure and the vaporpressure of atmosphere (e_(s)−e_(a)). When the percentage φ (%) of thevapor pressure e_(a) of atmosphere with respect to the saturated vaporpressure e_(s), that is, the so-called relative humidity is used,Expression 1 is rewritten as Expression 2. In order to increase thelatent heat flux L_(a), it is important that a refrigerant having alarge heat of evaporation ε is used, that the refrigerant is evaporatedin a condition of high saturated vapor pressure e_(s), and that thevapor pressure e_(a) of atmosphere in the vicinity of the cooling objectis reduced to lower the relative humidity φ.

$\begin{matrix}{L_{a} = {k \cdot ɛ \cdot e_{s} \cdot \left( {1 - \frac{\psi}{100}} \right)}} & (2)\end{matrix}$

The coefficient k which is the first term of the right side ofExpression 2, is considered to depend on refrigerant supply means(volume, film thickness, thermal conductivity, heat resistance, and thelike, of refrigerant), air supply means (density, specific heat, windvelocity, wind direction, and the like, of air), and the state of theevaporating surface of the heating element (refrigerant affinity,surface shape, surface treatment, and the like). It is necessary toincrease the coefficient k by facilitating the evaporation of therefrigerant from the heating element in such a way that the effectivearea of the evaporating surface is increased and the refrigerant isuniformly and thinly supplied.

When water having a relatively large heat of evaporation is taken as anexample of the refrigerant, the heat of evaporation ε of the second termcan be expressed by an approximate expression with respect totemperature t (° C.) as given by Expression 3. Even when the temperaturet is changed in a range from normal temperature to (° C.) to the boilingpoint of 100° C., the temperature dependency of the heat of evaporationε is relatively small.

ε=2502.3−2.4794t   (3)

When the refrigerant is water, the saturated vapor pressure e_(s) of thethird term is expressed by the Tetens formula as given by Expression 4.When the temperature t is elevated, the saturated vapor pressure e_(s)is almost exponentially increased. In order to increase the latent heatflux L_(a), it is effective to increase the ambient temperature t in thevicinity of the cooling object.

$\begin{matrix}{e_{s} = {6.11 \times 10^{\frac{7.5\; t}{t + 237.3}}}} & (4)\end{matrix}$

Similarly, when the refrigerant is water, the fourth term (1−φ/100) isexpressed by using the relative humidity φ_(o) (%) and the Tetensformula as given by Expression 5. In order to increase the value of thefourth term, it is necessary that the ambient temperature t is sethigher than the normal temperature t_(o), so as to lower the relativehumidity φ at temperature t, and to lower the vapor pressure e_(a) ofatmosphere.

$\begin{matrix}{{1 - \frac{\psi}{100}} = {1 - {\frac{\psi_{ο}}{100} \times 10^{\frac{7.5t_{ο}}{t_{ο} + 237.3} - \frac{7.5t}{t + 237.3}}}}} & (5)\end{matrix}$

FIG. 13 shows the dependency of the latent heat flux L_(a) on thetemperature t when water is used as the refrigerant. In the drawing, thecalculation is performed by such a way that Expression 3 to Expression 5are substituted in Expression 2, and that the normal temperature t_(o)is set to 20° C., the relative humidity φ_(o) is set to 60% RH, and thecoefficient k is set as a parameter. It is seen from FIG. 13 that thelatent heat flux L_(a) is increased as the temperature t is elevated.

In the evaporative cooling, a cooling temperature is determined in anequilibrium state between the heat generation density per unit area ofthe heating element and the latent heat flux L_(a) (heat removaldensity). In order to increase the amount of heat removed from theheating element and to increase the evaporative cooling efficiency, itis necessary to use a refrigerant having a large heat of evaporation eand to increase the area, from which the refrigerant is evaporated, sothat the latent heat flux L_(a) is increased on the basis of the abovedescribed method.

A feature of a typical embodiment according to the present invention isthat the area where the latent heat flux L_(a) is obtained and the totalamount of heat removed from the heating element are increased byattaching a vaporizing plate having an area larger than that of a heatgenerating portion of the heating element.

Another feature of the typical embodiment according to the presentinvention is that the coefficient k and the latent heat flux L_(a) areincreased by supplying the refrigerant liquid in a thin film manner andby increasing the effective area of the vaporizing plate in such a waythat the surface treatment and the shape processing, for increasingaffinity with the refrigerant, are performed to the surface of thevaporizing plate brought into contact with the heating element, or thatcapillaries are provided to the surface of the vaporizing plate.

Further, another feature is that the latent heat flux L_(a) is increasedby such a way that the saturated vapor pressure e_(s) in the vicinity ofthe vaporizing plate is increased and the relative humidity φ is reducedby supplying to the vaporizing plate warm air at the upper limittemperature or below of the heating element. It is also possible toobtain the effect of increasing the latent heat flux L_(a) by similarlysupplying to the vaporizing plate the refrigerant liquid at the upperlimit temperature or below of the heating element.

Further, another feature is that the latent heat flux L_(a) is increasedin such a way that the refrigerant liquid and air are respectivelysupplied from different directions with respect to the vaporizing plate,to thereby remove the saturated vapor layer on the surface of thevaporizing plate while maintaining the relative humidity φ at low, andto lower the vapor pressure e_(a) of atmosphere.

Further, another feature is that the size of the air supply system isreduced by eliminating the warm air generating mechanism in such a waythat in a configuration having first and second heating elements, warmair generated in the second heating element is supplied to thevaporizing plate of the first heating element.

Further, another feature is that the liquid supply system of therefrigerant is simplified in such a way that the refrigerant is suppliedto the vaporizing plate from a position higher than the heating elementby utilizing the weight of the refrigerant itself.

Further, another feature is that components of the liquid supply systemor the air supply system and the reflux system are reduced in such a waythat the liquid supply or the air supply is performed, by an exhaustsystem which forcibly exhausts the air containing the refrigerant vaporfrom the vaporizing plate, in the state where the pressure of thevaporizing plate side is made negative with respect to the normalpressure, and in such a way that the reflux is performed in the statewhere the pressure of the reflux side, in which the refrigerant vapor iscondensed from the exhaust and the condensed refrigerant liquid isreturned to the liquid supply system, is made positive.

Further, another feature is that the planar heating element issubstantially vertically arranged, and that the refrigerant liquid issupplied to the upper part of the vaporizing plate, and the aircontaining the refrigerant vapor and the residual refrigerant liquid aredischarged from the lower part of the vaporizing plate. Thereby, it ispossible to configure the liquid supply system or the discharge systemwhich is suitable for the vertical heating element, and in which thecooling system can be miniaturized.

Further, another feature is that the closed circuit system is configuredby the liquid supply system for supplying the refrigerant to thevaporizing plate, the exhaust system, and the reflux system whichreturns the refrigerant to the liquid supply system, and that the opencircuit system is configured by the air supply system for intaking airfrom ambient air, the exhaust system, and the reflux system fordischarging the air to ambient air. Thereby, it is possible to increasethe latent heat flux L_(a) by supplying air of a low vapor pressuree_(a) to the vaporizing plate by the use of ambient air in the simpleopen loop system, while circulating the refrigerant in the closedcircuit system.

Further, another feature is that the system for effecting reflux fromexhaust system through the primary heat exchange system is miniaturizedin such a way that the primary refrigerant vapor with heat taken fromthe heating element in the primary heat exchange system is cooled andcondensed by the secondary refrigerant, and that the heat absorbed bythe secondary refrigerant from the primary refrigerant vapor isdischarged in the secondary heat exchange system, and is that thecooling efficiency is improved by keeping the heat exhaust place in thesecondary heat exchange system away from the vicinity of the heatingelement.

Further, another feature is that the evaporative cooling is efficientlyperformed in such a way that a required amount of the refrigerant andair is supplied to the vaporizing plate by controlling the supply liquidamount, the supply liquid temperature, the supply air amount or thesupply air temperature according to the heat generation amount, thepower consumption, the operation rate, or the temperature of the heatingelement.

According to claims 1-5 of the present application, it is possible toefficiently perform the evaporative cooling even for a heating elementwith high heat generation density by increasing the latent heat fluxL_(a). According to claims 6-13 of the present application, it ispossible to effect the reduction in size and weight of the coolingsystem configured by the liquid supply system, the air supply system,the exhaust system, the reflux system, and the like. The presentinvention is particularly effective to increase the mounting density andto improve performance of major devices, such as a processor and an LSIin information platform devices, such as a server, a network, and astorage.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a view showing a configuration of an evaporative coolingsystem of a first embodiment according to the present invention;

FIG. 2 is a view showing a configuration of an evaporative coolingmodule of the first embodiment according to the present invention;

FIG. 3 is a sectional view of the evaporative cooling module of thefirst embodiment according to the present invention;

FIG. 4 is a view showing a configuration of a primary and a secondaryheat exchanger of the first embodiment according to the presentinvention;

FIG. 5 is a view showing a configuration of an evaporative coolingsystem of a second embodiment according to the present invention;

FIG. 6 is a view showing a configuration of an evaporative coolingsystem of a third embodiment according to the present invention;

FIG. 7 is a view showing a function of the evaporative cooling system ofthe first embodiment according to the present invention;

FIG. 8 is a view showing a function of the evaporative cooling system ofthe second embodiment according to the present invention;

FIG. 9 is a view showing a function of the evaporative cooling system ofthe third embodiment according to the present invention;

FIG. 10 is a view showing a function of an evaporative cooling system ofa fourth embodiment according to the present invention;

FIG. 11 is a view showing a function of an evaporative cooling system ofa fifth embodiment according to the present invention;

FIG. 12 is a view showing a function of an evaporative cooling system ofa sixth embodiment according to the present invention; and

FIG. 13 is an illustration of an evaporative cooling model according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following, embodiments of evaporative cooling systems accordingto the present invention will be described with reference to theaccompanying drawings.

FIG. 1 is a view showing a configuration of an evaporative coolingsystem of a first embodiment according to the present invention, and anexample in which the present invention is applied to a blade serversystem. The blade server system comprises a plurality of blade servers40, a back plane connected to the plurality of blade servers 40, an I/Omodule, a switch module, a storage module, a management module, a powersupply module, an air cooling fan module, and the like, and a serverchassis 41 for housing these components. The blade server 40 comprises aprocessor to which evaporative cooling modules 10 and 11 are attached, achip set 20, a memory module 21, a mother board 30, a connector 31 foreffecting connection with the back plane, and the like, and a case forcovering these components.

The evaporative cooling system comprises the evaporative cooling modules10 and 11 in contact with the processor which is a heating element, aliquid supply system which includes a liquid supply pump 50 and a liquidsupply tube 51, and which supplies a refrigerant liquid to theevaporative cooling modules 10 and 11, an air supply system whichincludes an air supply tubes 60 and 61, and which supplies air to theevaporative cooling modules 10 and 11, an exhaust system which includesan exhaust pump 70 and an exhaust tube 71, and which exhausts aircontaining a refrigerant vapor from the evaporative cooling modules 10and 11, a reflux system which includes a primary heat exchanger 80, areflux tube 81, and an exhaust port 82, and which condenses therefrigerant vapor and returns the condensed refrigerant liquid to theliquid supply system, and a heat exhaust system which includes asecondary heat exchanger 90, a water conveyance tube 91, and a waterreturning tube 92, and which discharges the heat absorbed from theprimary heat exchanger.

FIG. 2 is a view showing a configuration of the evaporative coolingmodule 10, and FIG. 3 is a sectional view of the evaporative coolingmodule 10. A processor package 100, to which the evaporative coolingmodule 10 is mounted, comprises a processor chip 101 which is a heatingelement, a cap 102 in close contact with the chip 101, and a packagesubstrate 103 to which the chip 101 is connected. The processor package100 is connected to the mother board 30 via a socket 104. Theevaporative cooling module 10 comprises a vaporizing plate 110 incontact with the cap 102 via a heat conducting material 105, a wick 111formed on a surface of the vaporizing plate 110, and a jacket 109 towhich the liquid supply tube 51, the air supply tube 60, and the exhausttube 71 are connected.

The heat generated by the processor chip 101 is conducted to thevaporizing plate 110 via the cap 102 and the heat conducting material105. The refrigerant liquid supplied from the liquid supply tube 51 isspread on the surface of the vaporizing plate 110 by a capillaryphenomenon of the wick 111 as shown by a liquid supply flow 112. Airwarmed by the heat generated by the chip set 20 and the memory module 21is sucked into an inside of the jacket 109 from the air supply tube 60by the exhaust pressure of the pump 70 as shown by an air supply flow113. The refrigerant liquid spread on the surface of the vaporizingplate 110 is evaporated into the warm air inside the jacket by the heatfrom the processor chip 101 as shown by an evaporative flow 115. The aircontaining the refrigerant vapor and the residual liquid of theunevaporated refrigerant liquid are discharged from the exhaust tube 71by the pump 70 as shown by an exhaust air and liquid flow 115.

FIG. 4 is a view showing a configuration of the primary heat exchanger80 and the secondary heat exchanger 90. The primary heat exchanger 80comprises a condenser which includes an insertion pipe 120 connected tothe exhaust tube 71 and a mantle pipe (cooling pipe) 121, and whichcondenses the refrigerant vapor in the exhaust air, a liquid tank 122which stores the condensed refrigerant liquid, a chamber 123 whichstores the residual air after condensation, and the exhaust port 82. Thesecondary heat exchanger 90 comprises a radiator 130 and a fan 131 whichair-cools the radiator. The cooling water is supplied from the secondaryheat exchanger 90 to the mantle pipe (cooling pipe) 121 by a waterconveyance pump 93 and the water conveyance tube 91, so as to cool therefrigerant vapor passing through the insertion pipe 120. The warm waterinto which the heat is absorbed from the refrigerant vapor is refluxedto the radiator 130 by the water returning tube 92, so as, to be cooled.The heat exhausted from the warm water is discharged to ambient air asshown by an exhaust heat flow 132.

FIG. 7 is a view showing a function of the evaporative cooling system ofthe first embodiment. The refrigerant liquid is fed to the evaporativecooling module 10 from the liquid supply system which comprises theliquid supply pump 50 and the liquid supply tube 51, and is evaporatedinto a refrigerant vapor inside the evaporative cooling module 10. Therefrigerant vapor is fed to the primary heat exchanger 80 from theexhaust system which comprises the exhaust pump 70 and the exhaust tube71, together with the residual liquid. The refrigerant vapor iscondensed in the heat exchanger 80, so as to be changed back to therefrigerant liquid. The refrigerant liquid is again fed to the liquidsupply system from the reflux system which comprises the primary heatexchanger 80 and the reflux tube 81. Thus, the refrigerant forms aclosed circuit circulatory system. The ambient air warmed by the chipset 20 is fed into the evaporative cooling module 10 from the air supplysystem including the air supply tube 60. The air containing therefrigerant vapor is fed to the primary heat exchanger 80 from theexhaust system, and the refrigerant vapor is condensed. The residual dryair is discharged from the exhaust port 82 to ambient air. Thus, the airsystem forms an open circuit system.

In the first embodiment configured as described above, the evaporativecooling is performed by obtaining the latent heat flux of about 4 W/cm²,for a processor having a maximum power consumption of about 100 W, theupper limit operating temperature of 65° C., and a package size ofapproximately 4 cm square, in such a way that water is used as arefrigerant liquid, the size of vaporizing plate 110 made of copper isset to about 5 cm square, and the supply air temperature is set toaround 40° C., under an atmosphere condition set at a usual room airtemperature of 25° C. and the indoor humidity of 60% RH. It isconsidered to use water or a fluorochemical inert fluid as therefrigerant material, but in the first embodiment, water having arelatively large heat of evaporation is used. In the first embodiment,the operation rate, the power consumption, the package temperature, orthe like, of the processor is monitored in correspondence with thevariation in the power consumption, that is, the heat generation amountof the processor. Thereby, the supply liquid amount and the supply airamount (exhaust air amount) are controlled according to these values.However, in addition to these, the supply liquid temperature and thesupply air temperature can also be used as the control factors. When aprocessor of different specifications about the maximum powerconsumption, the package size, and the like, is used, the refrigerantmaterial and the material, size, and the like, of the vaporizing plateare correspondingly designed in addition to the control factors. Asshown in FIG. 13, the supply liquid temperature and the supply airtemperature relate to the temperature t represented along the horizontalaxis, while the supply liquid amount and the supply air amount relate tothe coefficient k. The control and design may be performed inconsideration of these relationships.

In the first embodiment, the vaporizing plate 110 having an area largerthan that of the processor chip 101 which is the heating element isused. Thus, the heat is spread to the vaporizing plate, so as toincrease the region in which the latent heat flux can be obtained.Thereby, the evaporation can be promoted and the amount of removed heatcan be increased as compared with the case where the refrigerant isdirectly evaporated from the surface of the heating element 101 and thecap 102. In order to efficiently spread the evaporation region, a heatpipe and a vapor chamber may also be used as the vaporizing plate.Further, the wick 111 is stuck on the surface of the vaporizing plate110. The wick 111 is capillaries formed by fibers in a mesh form. Therefrigerant liquid is spread thinly and uniformly on the surface of thevaporizing plate 110 by the capillary phenomenon of the wick 111.Thereby, the heat resistance of the refrigerant liquid is reduced andthe effective area of the evaporation region is increased, so that thelatent heat flux can be increased. In order to obtain the same effect,instead of using the capillaries, an affinity coating and fine unevenprocessing may also be applied to the surface of the vaporizing plate110.

In the first embodiment, the intake ports of the air supply tubes 60 and61 are provided in the vicinity of the chip set 20 or the memory module21 around the processor chip 101. That is, the air supplied to theevaporative cooling modules 10 and 11 is the air subjected to the heatexchange with the chip set 20 or the memory module 21. Thereby, it ispossible to obtain the effect of cooling the memory module and the chipset, and the warmed air is supplied to the vaporizing plate 110. Whenthe temperature of air is elevated, the saturated vapor pressure isincreased. Thereby, the relative humidity is reduced and the latent heatflux is increased. Further, the heat generation in the chip set 20 andthe memory module 21 is utilized, and hence a heating mechanismexclusively used for warming the air need not be provided. The air istaken at a negative pressure from the air supply tubes 60 and 61 by thesuction of the exhaust pump 70, and thereby the air supply system can besimplified. Note that the temperature of the warm air does not exceedthe upper limit temperature of the processor chip 101, and hence thereis no problem for the operation and the reliability of the processorchip 101.

The refrigerant liquid is supplied to the vaporizing plate 110 from thedirection of the supply liquid flow 112, while the air is supplied tothe vaporizing plate 110 from the direction of the supply air flow 113.By supplying the air and the refrigerant liquid from the differentdirections, the relative humidity of the air can be kept low till thesurface of the vaporizing plate 110. Further, the saturated vapor layeron the surface of the vaporizing plate 110 is removed by the windpressure, and thereby the evaporation can be promoted. The refrigerantliquid is supplied to an upper part of the vaporizing plate 110 which isvertically erected. Thus, by the flow caused by the weight of therefrigerant liquid itself, and also by the capillary effect of the wick111, the refrigerant liquid is spread on the surface of the vaporizingplate 110, so as to be efficiently evaporated. Further, the unevaporatedresidual liquid is also automatically discharged by the weight of therefrigerant liquid itself, together with the refrigerant vapor, from alower part of the vaporizing plate 110. Thus, the liquid supply systemand the exhaust system can be simplified.

The refrigerant liquid is circulated through the closed circuit systemwhich is configured by the liquid supply system, the exhaust system, andthe reflux system, while the air is passed through the open circuitsystem in such a manner that the air taken from ambient air is passedthrough the air supply system, the exhaust system, the reflux system,and is then returned to ambient air. The air with low vapor pressure issupplied to the vaporizing plate 110 by using ambient air, and therebythe evaporation is promoted. The exhaust air with increased vaporpressure is fed to the reflux system, and the refrigerant vapor iscondensed. Thus, the air with reduced vapor pressure is returned toambient air. The refrigerant is circulated and hence need not befrequently replenished. When the refrigerant vapor is slightly leakedfrom the exhaust port 82 and thereby the volume of refrigerant in theliquid tank 122 is reduced, then the refrigerant for evaporative coolingmay be automatically replenished to the liquid tank 122 from the waterconveyance tube 91 or the water returning tube 92 through a bypass pipe,by utilizing that the refrigerant for evaporative cooling is the same asthe refrigerant of the secondary heat exchanger.

The heat flow is in such a manner that the heat generated from theprocessor chip 101 is successively conducted to the cap 102, the heatconducting material 105, and the vaporizing plate 110, and istransferred to the refrigerant vapor as the latent heat, that therefrigerant vapor is fed through the exhaust system and is condensed inthe condenser of the primary heat exchanger 80, and that the latent heatis transferred to the cooling water in the secondary heat exchanger 90,and is discharged to ambient air as the exhaust heat flow 132 from theradiator 130. The refrigerant vapor is cooled and condensed by the watercooling using the condensers 120 and 121 more efficiently than the aircooling. Thus, the primary heat exchanger 80 is miniaturized, so as tobe able to be provided, for example, in a part of a server rack, a sidepanel, a back panel, or the like. Further, the primary heat exchanger 80is separated from the secondary heat exchanger 90 which is the placewhere the heat is discharged to ambient air. Thus it is possible that aserver rack in which a server chassis 41 and the primary heat exchanger80 are housed is installed in an indoor place, such as in a room of datacenter, and the secondary heat exchanger 90 is installed in an outdoorplace. As a result, the indoor air conditioning load, that is, the airconditioning power can be reduced without raising the temperature in theroom.

FIG. 5 is a view showing a configuration of an evaporative coolingsystem of a second embodiment according to the present invention. FIG. 8is a view showing a function of the evaporative cooling system of thesecond embodiment. Here, the present invention is applied to the bladeserver system is shown similarly to the case of the first embodiment.The evaporative cooling system of the second embodiment is differentfrom the first embodiment in that the air supply system is configured bya warm air blower 62 and the air supply tubes 60 and 61, and that theexhaust system is configured by the exhaust tube 71.

In the second embodiment, the evaporative cooling modules 10 and 11 areattached to the processor, the refrigerant liquid is evaporated from thevaporizing plate having an area larger than that of the processor chipand having capillaries on the surface thereof. The refrigerant liquid issupplied from an upper part of the evaporative cooling modules 10 and 11via the liquid supply tube 51. The warm air is supplied to the modules10 and 11 via the air supply tubes 60 and 61 from the directiondifferent from the direction in which the refrigerant liquid issupplied. The refrigerant vapor and the residual liquid are dischargedfrom a lower part of the modules 10 and 11. The condensed refrigerantliquid collected by the primary heat exchanger 80 is again returned tothe modules 10 and 11 through the liquid supply pump 50. The refrigerantis circulated in the closed circuit circulatory system, while the air ispassed through in the open circuit system from the warm air blower 62 tothe discharge opening 82 of the primary heat exchanger 80. In thesecondary heat exchanger 90, the heat absorbed by the refrigerant vaporfrom the processor is eventually discharged to ambient air via thecooling water and the radiator.

According to the second embodiment, the warm air at the upper limitoperating temperature or below of the processor chip which is theheating element is supplied to the evaporative cooling modules 10 and 11from the warm air blower 62. Thereby, the saturated vapor pressureinside the modules is increased, so as to facilitate the evaporation ofthe refrigerant liquid supplied from the liquid supply pump 50. The aircontaining the refrigerant vapor and the unevaporated residual liquidare discharged from the evaporative cooling modules 10 and 11 by the airsupply pressure of the warm air blower 62, and hence the exhaust pump 70can be eliminated from the exhaust system. The latent heat flux, thatis, the cooling capacity is accurately controlled to the variation inthe heat generation amount of the processor, in such a way that thesupply air temperature and the supply air amount (wind velocity) of thewarm air blower 62 are changed according to the operation rate, thepower consumption, the package temperature, or the like, of theprocessor.

FIG. 6 is a view showing a configuration of an evaporative coolingsystem of a third embodiment according to the present invention. FIG. 9is a view showing a function of the evaporative cooling system. In thethird embodiment, a blade chassis 42 is provided inside the serverchassis 41, and the plurality of blade boards 30 is enclosed in theinside of the blade chassis 42. The evaporative cooling is performedinside the blade chassis 42, and hence liquid-proof treatment againstthe refrigerant liquid, which treatment also serves as the affinitycoating, is applied to the surfaces of the board 30, the vaporizingplates 110 and 116 attached to the processor, the chip set 20, thememory module 21, the connector 31, and the like.

The refrigerant liquid is supplied to an upper surface of the bladechassis 42 from the liquid supply system which is configured by theliquid supply pump 50 and the liquid supply tube 51. The air warmed bythe heat generated by the components (an I/O module, a switch module, astorage module, a management module, a power supply module, and thelike) other than the blade server is taken into the inside of the bladechassis 42 from an air supply port 63 by the exhaust pressure of theexhaust pump 70. The refrigerant liquid is evaporated from thevaporizing plates 110 and 116, the chips 20 and 21, and the like, whichare mounted on the board 30. The refrigerant vapor and the unevaporatedresidual liquid are discharged from the lower surface of the evaporativecooling chassis 42 by the exhaust system which is configured by theexhaust pump 70 and the exhaust tube 71. The refrigerant liquid iscirculated to the liquid supply system through the primary heatexchanger 80 and the reflux tube 81. The residual air is exhausted fromthe exhaust port 82.

According to the third embodiment, the evaporative cooling can beperformed not only to the processor but also to the peripheral chips onthe board 30. Thus, it is not necessary to provide the evaporativecooling module, the liquid supply tube, and the air supply tube for eachprocessor. Also, the air cooling fan for cooling the peripheral chipscan be eliminated. As a result, it is possible to reduce the weight ofthe blade server system. Note that the vaporizing plate is attached tothe processor in the third embodiment, but the vaporizing plate may beattached to the peripheral chip according to the heat generation amountof the peripheral chip. Further, it is possible to attach a commonvaporizing plate over a plurality of chips, and also possible to providea vaporizing plate serving as a liquid-proof cover.

FIG. 10 is a view showing a function of the evaporative cooling systemof a fourth embodiment according to the present invention. The basicconfiguration of the fourth embodiment is the same as that of the secondembodiment. But the configuration of embodiment 4 is different that ofthe second embodiment in that the warm air blower 62 intakes warm airfrom the chamber of the primary heat exchanger 80 via a suction tube 64,and feeds the warm air from the air supply tube 60 to the evaporativecooling module 10. The primary heat exchanger 80 has no exhaust port.Thus, there are configured a closed circuit circulatory system forcirculating air through the warm air blower 62, the air supply tube 62,the evaporative cooling module 10, the exhaust tube 71, the primary heatexchanger 80, and the suction tube 64, and a closed circuit circulatorysystem for circulating the refrigerant through the air supply pump 50,the air supply tube 51, the module 10, the exhaust tube 71, the primaryheat exchanger 80, and the reflux tube 81.

According to the fourth embodiment, closed circuit systems areconfigured for both the refrigerant and air. Thus, even when therefrigerant vapor is slightly mixed in the air after the refrigerantvapor is condensed in the primary heat exchanger 80, it is possible toprevent the loss of the refrigerant as compared with the cases in thefirst embodiment and the second embodiment. The residual air after therefrigerant vapor is condensed is fed to the warm air blower 62. Thus,the dry air whose saturated vapor pressure is increased and whoserelative humidity is reduced, is supplied to the evaporative coolingmodule 10, so as to thereby promote the evaporation.

FIG. 11 is a view showing a function of an evaporative cooling system ofa fifth embodiment according to the present invention. The basicconfiguration of the fifth embodiment is similar to that of the firstembodiment. However, the configuration of the fifth embodiment isdifferent from that of the first embodiment in that the refrigerantliquid is warmed by a liquid warming heater 52 in the liquid supplysystem, and that the warm liquid at the upper limit temperature or belowof the processor is supplied to the evaporative cooling module 10.Similarly to the effect obtained by supplying the warm air and warm windin the first embodiment and the second embodiment, by supplying the warmliquid, the saturated vapor pressure is increased and also the relativehumidity is reduced in the vicinity of the vaporizing plate inside themodule 10, so that the vaporization efficiency is improved.

The liquid warming heater 52 may be provided side by side with theliquid supply pump 50. In the air supply system, the air warmed by theheat generated by the peripheral chip may be supplied in a mannersimilarly to the case of the first embodiment. However, when the effectto promote the evaporation by the warm liquid is enough for the heatgeneration amount, it is not necessary to warm the air by the heatgenerated by the peripheral chip. That is, it is also possible to changethe direction of the intake port of the air supply tube 60.

FIG. 12 is a view showing a function of an evaporative cooling system ofa sixth embodiment according to the present invention. In the sixthembodiment, the pressure on the side of the evaporative cooling module10 is made negative by using the exhaust pressure of the exhaust pump70, and thereby the warm air is supplied to the vaporizing plate fromthe air supply tube 60. Also, the pressure on the side of the primaryheat exchanger 80 is made positive, and thereby the refrigerant liquidis fed to a liquid supply tank 53 from the reflux tube 80. In theprimary heat exchanger 80, when the valve of the exhaust port 82 is setin the closed state, the internal pressure of the chamber is increasedby the exhaust air and the exhaust liquid, so as to make the refrigerantliquid flow into the reflux tube 81 from the liquid tank. The liquidsupply tank 53 is placed higher in level than the evaporative coolingmodule 10. Thus, the refrigerant liquid is made to flow down from theliquid supply tank 53 to the module 10 by the weight of the refrigerantliquid itself, so as to be supplied to the vaporizing plate brought incontact with the processor 100.

According to the sixth embodiment, the liquid supply pump can beeliminated from the liquid supply system by using the exhaust pressureof the exhaust pump and the weight of the refrigerant liquid itself.Thus, it is possible to reduce the power required for the coolingsystem, and also possible to reduce the size of the blade server system.

The evaporative cooling system according to the present invention issuitable for information platform devices, such as a server, a network,and a storage which are required to have higher performance and higherdensity. The evaporative cooling system according to the presentinvention can be widely applied to cool an apparatus having a heatingelement, such as, for example, electronic devices such as a PC and aportable telephone, power devices such as a generator and a fuel cell,and dynamic devices such as a motor vehicle and a railroad vehicle.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An evaporative cooling system for cooling a heating element by usingheat of evaporation of a refrigerant, comprising: a vaporizing platehaving an area larger than a heat generating portion of the heatingelement, and configured to dissipate heat by being brought into contactwith the heat generating portion and to evaporate the refrigerant liquidinto a refrigerant vapor; a liquid supply system to supply therefrigerant liquid to the vaporizing plate; an air supply system tosupply air to the vaporizing plate; an exhaust system to exhaust aircontaining the refrigerant vapor around the vaporizing plate; and areflux system to condense the refrigerant vapor of the exhaust system tocollect the condensed refrigerant liquid, and to return the collectedrefrigerant liquid to the liquid supply system.
 2. The evaporativecooling system according to claim 1, wherein the vaporizing plate hasone surface in contact with the heat generating portion of the heatingelement and the other surface having affinity with the refrigerantliquid or covered with capillaries.
 3. The evaporative cooling systemaccording to claim 1, wherein the air supply system supplies, to thevaporizing plate, warm air at a temperature lower than the upper limittemperature of the heating element.
 4. The evaporative cooling systemaccording to claim 1, wherein the liquid supply system supplies, to thevaporizing plate, the refrigerant liquid at a temperature lower than theupper limit temperature of the heating element.
 5. The evaporativecooling system according to claim 1, wherein the air supply systemsupplies air to the vaporizing plate from a direction different from adirection in which the refrigerant liquid is supplied to the vaporizingplate by the liquid supply system.
 6. An evaporative cooling system forcooling a first and a second heating element, comprising: a vaporizingplate to be brought into contact with the first heating element and toevaporate a refrigerant liquid into a refrigerant vapor; a liquid supplysystem to supply the refrigerant liquid to the vaporizing plate; anintake and exhaust system to intake air in the vicinity of the heatingelements to supply the air to the vaporizing plate, and to exhaust aircontaining the refrigerant vapor from the vaporizing plate; and a refluxsystem to condense the refrigerant vapor from the exhausted air tocollect the refrigerant liquid, and to return the collected refrigerantliquid to the liquid supply system.
 7. The evaporative cooling systemaccording to claim 6, wherein the liquid supply system supplies therefrigerant liquid to the vaporizing plate from a place higher in levelthan the vaporizing plate by using the weight of the refrigerant liquiditself.
 8. The evaporative cooling system according to claim 6, whereinthe exhaust system includes a pump for, by performing a forced exhaust,setting a side of the vaporizing plate to a negative pressure andsetting a side of the reflux system to a positive pressure.
 9. Anevaporative cooling system comprising: holding means to hold a planarheating element in a substantially vertical state; a vaporizing plate tobe brought into contact with the heating element and to evaporate arefrigerant liquid into a refrigerant vapor; a liquid supply system tosupply the refrigerant liquid to the vaporizing plate; an air supplysystem to supply air to the vaporizing plate; an exhaust system toexhaust air containing the refrigerant vapor from the vaporizing plate;and a reflux system to condense the refrigerant vapor of the exhaustsystem to collect the condensed refrigerant liquid, and to return thecollected refrigerant liquid to the liquid supply system.
 10. Theevaporative cooling system according to claim 9, wherein the exhaustsystem discharges a residual liquid of the refrigerant liquid from thevaporizing plate, together with air containing the refrigerant vapor.11. An evaporative cooling system for cooling a heating element by usingheat of evaporation of a refrigerant, comprising: a vaporizing plate tobe brought into contact with the heating element and to evaporate arefrigerant liquid into a refrigerant vapor; a liquid supply systemto-supply the refrigerant liquid to the vaporizing plate; an air supplysystem to intake air from ambient air and to send the air to thevaporizing plate; an exhaust system to exhaust air containing therefrigerant vapor from the vaporizing plate; and a reflux system tocondense the refrigerant vapor from the exhaust air to return thecondensed refrigerant liquid to the liquid supply system, and todischarge residual air to ambient air, wherein the refrigerant iscirculated in a closed circuit which is configured by the liquid supplysystem, the exhaust system, and the reflux system, and wherein air iscirculated in an open circuit which is configured by the air supplysystem, the exhaust system, and the reflux system.
 12. An evaporativecooling system for cooling a heating element by using heat ofevaporation of a refrigerant, comprising: a vaporizing plate to bebrought into contact with the heating element and to evaporate a firstrefrigerant liquid into a first refrigerant vapor; a liquid supplysystem to supply the first refrigerant liquid to the vaporizing plate;an air supply system to send air to the vaporizing plate; an exhaustsystem to exhaust air containing the first refrigerant vapor from thevaporizing plate; a primary heat exchange system to cool air of theexhaust system by a second refrigerant liquid to condense the firstrefrigerant vapor, and to collect the condensed first refrigerantliquid; a reflux system to return the first refrigerant liquid from theprimary heat exchange system to the liquid supply system; and asecondary heat exchange system to discharge heat absorbed by the secondrefrigerant liquid from the first refrigerant vapor.
 13. An evaporativecooling system for cooling a heating element by using heat ofevaporation of a refrigerant, comprising: a vaporizing plate to bebrought into contact with the heating element and to evaporate arefrigerant liquid into a refrigerant vapor; a liquid supply system tosupply the refrigerant liquid to the vaporizing plate; an air supplysystem to supply air to the vaporizing plate; an exhaust system toexhaust air containing the refrigerant vapor in the vicinity of thevaporizing plate; and a reflux system to condense the refrigerant vaporof the exhaust system to collect the refrigerant liquid, and to returnthe collected refrigerant liquid to the liquid supply system, whereinthe liquid supply amount, the liquid supply temperature, the air supplyamount, or the air supply temperature is controlled according to theheat generation amount, the power consumption, the operation rate, orthe temperature, of the heating element.